A catalyst comprising titanium oxide as an essential ingredient exhibits high activity and high durability in a denitration process using ammonia or urea, and therefore has been widely used domestically and internationally. In this denitration catalyst, denitration performance is reduced, during use for a long period of time, due to adhesion of a catalyst poison such as an alkaline component, arsenic, phosphorus or the like that is contained in an exhaust gas, coarsening of catalyst particles by sintering, or the like. When the denitration performance is reduced, the catalyst is replaced with a new denitration catalyst. Upon this replacement, a large amount of used denitration catalyst is produced. The used denitration catalyst is regenerated to reduce a waste material, catalyst production cost and the like.
As a method for regenerating a used denitration catalyst, for example, Patent Literature 1 discloses a method comprising dissolving a used titania solid catalyst in a mineral acid, heating the obtained solution to cause hydrolysis thereof, and subsequently neutralizing the resulting product by alkali.
Patent Literature 2 discloses a method comprising preparing a slurry composed of water, sulfuric acid and/or salts of sulfuric acid, and a catalyst component powder comprising any of titanium oxide and vanadium oxide; titanium oxide, vanadium oxide and molybdenum oxide; titanium oxide, vanadium oxide and tungsten oxide; or titanium oxide, vanadium oxide, molybdenum oxide and tungsten oxide, and coating the slurry, by a spray method or an immersion method, on a surface of a low active denitration catalyst to which an alkaline metal element or an alkaline earth metal element adheres,
Patent Literature 3 discloses a method comprising making oxalic acid supported on a used denitration catalyst composed of a metallic substrate comprising iron such as a metal lath or the like and a denitration catalyst component, treating the resulting product with a solution comprising an ammonium salt of tungstic acid, and subjecting the treated product to a drying process.
Patent Literature 4 discloses a method comprising impregnating water into a used denitration catalyst comprising titanium oxide, vanadium oxide, tungsten oxide or molybdenum oxide, and aluminum sulfate as an essential ingredient, heat-treating the impregnated catalyst at not less than 50° C. and not more than 100° C. to hydrolyze the aluminum sulfate in the catalyst, and then washing the resulting catalyst with water.